Considering that charging over USB can take around 5 hours (to only 1-2 hours it would take from the wall mounted plug), can it be harmful for the smartphone battery if it's always charged from USB?

  • Charging from a computer over USB may actually be better than fast charging from a wall socket. Reason1) Batteryuniversity has shown that Lithium Ion batteries that are charged too fast will die sooner. Reason2) Charging slower will not heat the battery as much, which can prolong battery life
    – Sepero
    Commented Nov 18, 2012 at 11:27
  • Been charging my Lumia 710 most of the time through USB, and have been noticing increased battery life over the past weeks.
    – user27654
    Commented Jan 31, 2013 at 21:00

2 Answers 2


I don't see how the duration of the charge would relate to whether or not it's harmful to the smartphone. I have never seen any documentation that keeping a phone plugged in perpetually (whether plugged into USB, AC or DC) would cause any harm to the phone itself. An argument could be made that it's harmful to the battery.

Constant charging is not generally a problem for Lithium Ion Polymer batteries (which most new cell phone batteries are). It is in fact better to frequently charge them, and not let them fully discharge.

One factor that does degrade the battery life of all Lithium Ion batteries is heat. The more heat it's exposed to the faster it will lose capacity, so I can see how keeping it plugged in may keep it warmer longer and theoretically degrade the battery life.

Here are a couple good resources discussing battery life:

  1. http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
  2. http://www.droidforums.net/forum/tech-issues-bug-reports-suggestions/1974-understanding-battery-life.html
  • Excellent answer, thank you. I meant battery as well.
    – Francisc
    Commented Jan 29, 2011 at 22:32
  • 6
    I believe the slower charge from USB would keep the battery temp lower than a faster charge, so it may actually be beneficial.
    – TomG
    Commented Jan 30, 2011 at 0:48

The issue is to not let the battery specifically lithium battery be full changed and not let it completely discharge . let it be between 40 to 80 percent. by using USB is more suitable because it let the battery to be slowly charged with significant absence of heat to damage the battery. Thanks

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